Guyton & Hall – Figure 45.2 Fundamentals of Nervous System

General Design of Nervous System:

Analogy = Computer

Processing = Integrative System Input = Sensory System • 99% of sensory information Output = Motor System discarded Receptors: Effectors: • Synapses determine pathway Tactile of signals Skeletal muscle Visual • Information stored for future use Smooth muscle Auditor Glandular secretion Memory: Olfactory Highly facilitated synaptic pathways (sensory input not required to excite pathway)

Fundamentals of Nervous System Fundamentals of Nervous System

Organization of Nervous System: Histology of Nervous System:

A. Neuroglia (supporting cells – “nerve glue”) Nervous system

Central Nervous System (CNS) ciliated Integration (most common) Central nervous system Peripheral nervous system (CNS) (PNS) Motor Sensory output input

Brain Spinal cord Motor division Sensory division Astrocytes: Microglia: Ependymal cells: (efferent) (afferent) • anchor neurons to capillaries • macrophages; engulf invaders • line canals / ventricles of brain • repair damaged neural tissue • produce (CSF) • maintain “blood / brain barrier”

Autonomic nervous system Somatic nervous system Peripheral Nervous System (PNS) (involuntary; smooth & cardiac muscle) (voluntary; skeletal muscle) Schwann cells: • Insulate neurons (myelin sheath)

Sympathetic division Parasympathetic division Oligodendrocytes: Satellite cells: • Insulate neurons (myelin sheath) • Function similar to astrocytes

Fundamentals of Nervous System Fundamentals of Nervous System

Histology of Nervous System: • Long-lived (~ 100 years) Histology of Nervous System: • Long-lived (~ 100 years) • High metabolic rate • High metabolic rate B. Neurons B. Neurons • Specialized “excitable” cells • Specialized “excitable” cells • Allow for communication throughout body (via electrical impulses) • Allow for communication throughout body (via electrical impulses)

Neuron Anatomy: Functional Classification of Neurons:

1) Dendrites: Receive information (environment / other neurons) 1) Sensory (Afferent) neurons: 2) Cell body (soma): Integrates information / initiate response • Carry information from sensory receptors to CNS

3) Axon: Conducts action potential (AP – electrical impulse) 2) Motor (Efferent) neurons: 4) Synaptic terminals: Transmit signal (other neurons / effector organs) • Carry information from CNS to effector organs

3) Association neurons (Interneurons): Axon hillock (AP generation) • Interconnects neurons in brain / spinal cord Axon Dendrites Synaptic terminals Schwann Cells (PNS) Centrioles

(Can not divide) Cell body

1 Fundamentals of Nervous System

Histology of Nervous System: • Long-lived (~ 100 years) Central Nervous System • High metabolic rate B. Neurons • Specialized “excitable” cells • Allow for communication throughout body (via electrical impulses)

Structural Classification of Neurons (# of processes) :

Multipolar Bipolar Unipolar ( 3 processes) (2 processes) (1 process)

Axon Axon Axon

Dendrites Trigger zone Dendrites Trigger zone Trigger zone

Dendrites

• Motor neurons • Sensory neurons • Sensory neurons • Interneurons (e.g., special sense organs) (PNS)

Central Nervous System Central Nervous System

Organization of Nervous System: Brain: No correlation exists between brain size and intelligence… • ~ 3.5 lbs (35 billion neurons) Nervous system • ♂ brain ~ 10% larger than ♀ brain

Integration Central nervous system Peripheral nervous system Gross Anatomy: (forebrain) (CNS) (PNS) Motor Sensory output input

Brain Spinal cord Motor division Sensory division (efferent) (afferent) Diencephalon (midbrain)

Autonomic nervous system Somatic nervous system (involuntary; smooth & cardiac muscle) (voluntary; skeletal muscle)

Brainstem () Sympathetic division Parasympathetic division

Marieb & Hoehn – Figure 12.1 Marieb & Hoehn – Figure 12.2 Central Nervous System Central Nervous System

Embryonic Development of Brain: Embryonic Development of Brain: How we will consider brain anatomy

3 week old embryo 5 week old embryo

Neural Primary brain vesicles Secondary brain vesicles Adult brain structures tube Neural crest

Neural plate Step 3: Telencephalon Cerebrum (endbrain) Neural fold cells migrate; form neural crest Step 1: • Neural crest gives rise to PNS Anterior Proencephalon Diencephalon Diencephalon Neural plate forms from surface ectoderm (forebrain) (interbrain)

4 week old embryo Mesencephalon Mesencephalon Brain stem (midbrain) Neural fold (midbrain) (midbrain)

Metencephalon Brain stem () Rhombencephalon (afterbrain) (hindbrain) Cerebellum Myelencephalon (spinalbrain) Brain stem (medulla) Posterior Neural groove Neural tube Spinal cord Step 2: Step 4: Neural plate invaginates; forms neural groove Neural groove becomes neural tube; sinks deep • Neural folds flank neural groove • Neural tube gives rise to CNS

2 Central Nervous System Central Nervous System Nuclei: Space restriction greatly affects Groups of cell bodies located in Embryonic Development of Brain: brain development Basic Layout of Neurons: the central nervous system (analogous to ganglia in PNS) Brain stem (pons) Brain stem (midbrain) White matter: Regions of myelinated axons in CNS Cerebellum Midbrain Gray matter: Regions of unmyelinated axons / cell bodies in CNS flexure

Diencephalon Brain stem (medulla) Cortex White White Gray matter Cerebrum matter Gray matter Cervical flexure matter 5 week old embryo 13 week old embryo • Flexures develop to fit rapidly growing brain into membranous skull • Cerebrum forced to grow posterior and lateral (‘horseshoe’) Nucleus

Spinal cord Cerebrum

• Convolutions develop to • Basic pattern observed in CNS • Cortex formed by migration of neurons Newborn increase surface area 26 week old embryo • Cerebellum similar to cerebrum in its external cortex of brain Marieb & Hoehn – Figure 12.3 Marieb & Hoehn – Figure 12.4

Marieb & Hoehn – Figure 12.5 Central Nervous System Central Nervous System

Brain Anatomy: CSF Circulation: Presence of CSF in subarachnoid space A. Ventricles: Hollow chambers enclosed within brain (continuous with each other…) Arachnoid villus gives buoyancy to brain (97% weight reduction)

Lateral ventricle Cerebrospinal fluid (CSF) 1) CSF produced by in • Provide constant, controlled environment ventricles for brain cells 2) CSF flows through ventricles and into • Protect brain from toxins subarachnoid space via lateral and • Prevent escape of local neurotransmitters median apertures Choroid plexus: 3) CSF exits subarachnoid space via arachnoid villi Vascular network; produces CSF

Fourth ventricle • Similar ion composition to blood plasma Central canal •  protein content Median aperture

Ventricles lined with ependymal cells (circulate CSF)  Lumbar puncture • Gasses cross freely (spinal tap) • 0.5 L / day produced (‘water on the brain”) Costanzo – Figure 3.36 Marieb & Hoehn – Figure 12.26

Central Nervous System Central Nervous System ~ 85% of brain mass

Brain Anatomy:

B. Cerebrum (cerebral hemispheres): Central sulcus

Cerebrum Parietal (forebrain) Frontal lobe lobe Parieto-occipital sulcus

Diencephalon (midbrain)

Gyrus Sulcus Occipital (ridge) (groove) lobe Insula Brainstem Cerebellum (hindbrain)

Temporal lobe Lateral Fissure sulcus (deep groove) Marieb & Hoehn – Figure 12.6

3 Central Nervous System Central Nervous System

Brain Anatomy: Brain Anatomy: The cerebral B. Cerebrum (cerebral hemispheres): B. Cerebrum (cerebral hemispheres): cortex is the 1) Cerebral cortex: seat of conscious behavior Basic regions: Cerebral cortex Cerebral • Contains 3 types of functional areas: (superficial to deep) white matter 1) Motor areas (send output) Only 2 - 4 mm thick but comprises 40% 1) Cerebral cortex (gray matter) 2) Sensory areas (receive input) of the brain’s mass 2) Cerebral white matter 3) Association areas (interpret data) 2.5 ft2 of surface area 3) Basal nuclei

Corpus callosum: Functional MRI scan White tract connecting (measure blood flow) cerebral hemispheres

Basal nuclei Neural cartography (electrostimulation)

Marieb & Hoehn – Figure 12.8 Central Nervous System Central Nervous System

Brain Anatomy: Homunculus (“little man”): Primary motor B. Cerebrum (cerebral hemispheres): Note: cortex One-to-one correspondence between 1) Cerebral cortex: Conscious control of skeletal cortical neurons and muscles misleading; muscle movements map really “fuzzy” • Motor areas:

Somatotopic mapping: The entire body is spatially represented in the cerebral cortex Pyramidal cells extend long axons to the spinal cord, forming pyramidal

tracts, or corticospinal tracts Marieb & Hoehn – Figure 12.9

Marieb & Hoehn – Figure 12.8 Marieb & Hoehn – Figure 12.8 Central Nervous System Central Nervous System

Brain Anatomy: Brain Anatomy: Primary somatorsensory Primary motor cortex B. Cerebrum (cerebral hemispheres): B. Cerebrum (cerebral hemispheres): cortex Receives information from Spatial sensory receptors in skin & 1) Cerebral cortex: Conscious control of skeletal 1) Cerebral cortex: discrimination communicates proprioreceptors in joints muscle movements directly with • Motor areas: primary motor cortex • Sensory areas: Somatosensory Frontal eye field association Gustatory cortex Controls voluntary Premotor cortex cortex Receives / interprets movement of eyes Controls learned motor Integrates / interprets sensations of taste skills of repetitious somatosensory inputs or patterned nature (e.g., temp. / pressure) (e.g., typing) Primary visual Primary auditory cortex cortex Receives visual Receives auditory information information Broca’s area Medial (retinotopic mapping) (tonotopic mapping) Controls muscles involved in speech production Visual Auditory association (often more pronounced in Association area one hemisphere of brain) Olfactory cortex area Integrates / interprets Integrates / interprets Receives olfactory auditory inputs visual inputs information (e.g., music / thunder) (e.g., color / form) • Part of rhinencephalon (‘nose brain’)

4 Marieb & Hoehn – Figure 12.8 Central Nervous System Central Nervous System Phrenology: Brain Anatomy: Phineus Gage (1823 – 1860) The brain is the organ of the mind; Locations where sensations, thoughts, contains localized, specific modules B. Cerebrum (cerebral hemispheres): and emotions become conscious Franz Gall 1) Cerebral cortex: (makes us who we are…) (1758 – 1828)

• Association areas (multimodal): The American Crowbar Case (matures slowly) Anterior association area Introduction (Prefrontal cortex) • Intelligence • Complex learning • Recall • Personality

Marieb & Hoehn – Figure 12.8 Central Nervous System Central Nervous System

Brain Anatomy: Brain Anatomy: Locations where sensations, thoughts, The cerebral B. Cerebrum (cerebral hemispheres): B. Cerebrum (cerebral hemispheres): and emotions become conscious cortex is the 1) Cerebral cortex: (makes us who we are…) 1) Cerebral cortex: seat of conscious behavior • Association areas (multimodal): • Contains 3 types of functional areas • Contralateral control (e.g., left hemisphere controls right body) Only 2 - 4 mm thick but comprises 40% Anterior association Posterior association Decussation: of the brain’s mass area area Location where neural pathways cross 2 • Pattern recognition 2.5 ft of surface area • Spatial recognition • Occur at different locations in CNS • Sensory grouping • Language centers • Lateralization (i.e., hemisphere specialization) (Wernicke’s area)

Limbic association area Processes emotions related to personal / social interactions

Central Nervous System Central Nervous System

Brain Anatomy:

B. Cerebrum (cerebral hemispheres):

Basic regions: Cerebral cortex Cerebral (superficial to deep) white matter

1) Cerebral cortex (gray matter) 2) Cerebral white matter 3) Basal nuclei

Basal nuclei Categorical Representational

5 Central Nervous System Central Nervous System

Brain Anatomy: Brain Anatomy:

B. Cerebrum (cerebral hemispheres): Commissural B. Cerebrum (cerebral hemispheres): Association fibers 2) Cerebral white matter: fibers Basic regions: Fiber tracts responsible for communication Cerebral cortex Cerebral (superficial to deep) white matter between cerebral areas and lower CNS 1) Cerebral cortex (gray matter)

A) Commissural Fibers (form commissures) : 2) Cerebral white matter • Interconnect cerebral hemispheres 3) Basal nuclei B) Association Fibers: • Interconnect areas of neural cortex within a single hemisphere

C) Projection Fibers: • Interconnect cerebral hemispheres with other regions of the brain

Corona radiata: Projection Internal capsule: Point where projection fibers radiate fan-like fibers Compact band of projection Basal nuclei through cerebral white matter fibers near diencephalon

Marieb & Hoehn – Figure 12.10

Central Nervous System Central Nervous System

Brain Anatomy:

B. Cerebrum (cerebral hemispheres): 3) Basal nuclei: Cerebrum • Composed of gray matter (neuron cell bodies) (forebrain) • Function: 1) Subconscious control of skeletal muscle tone 2) Control stereotypical motor movements (e.g., arm swing) • Regulate intensity / inhibit unnecessary movements

Diencephalon (midbrain) Caudate nucleus

Putamen Corpus striatum Brainstem Cerebellum Lentiform (hindbrain) Striped appearance nucleus due to passage of Globus internal capsule fibers pallidus

Central Nervous System Central Nervous System “Emotional brain” Brain Anatomy: Brain Anatomy: Diencephalon structures: Thalamus C. Diencephalon: Limbic system (functional brain system): • Thalamus (anterior thalamic nuclei) “Gateway to the • Hypothalamus Thalamus: cerebral cortex” Cerebral cortex structures: • Composes 80% of diencephalon • Cingulate gyrus • Relay station for all information • Parahippocampal gyrus entering / exiting the cerebral cortex • Hippocampus • Amygdala Hypothalamus: Fornix: Fiber tract linking • Autonomic control center regions together • Center for emotional response • Body temperature regulation • Regulation of food / water intake • Regulation of sleep-wake cycles Hypothalamus • Control of endocrine system  Alzheimer’s Disease: Epithalamus: • Control emotional states (e.g., fear) / behavioral drives (e.g., sex drive) Progressive degenerative disease of the brain Epithalamus • Link conscious (cerebral cortex) with unconscious function (brain stem) • Houses (melatonin) • Memory loss and choroid plexus (forms CSF) • Psychosomatic illnesses = emotion-induced illness • Disorientation “Control center • Long-term memory storage / retrieval • Moodiness / confusion of body” Marieb & Hoehn – Figure 12.12 / 12.13

6 Central Nervous System Central Nervous System

Brain Anatomy:

D. Brain stem: • Deep gray matter; superficial white matter Cerebrum (forebrain) • Produce rigidly programmed, autonomic behaviors necessary for survival • Conduction pathways between higher Thalamus and lower brain centers Midbrain: Diencephalon Midbrain (midbrain) • Visual / auditory reflex centers Pons: • Regulate respiration rate / depth

Medulla oblongata: Pons Brainstem Cerebellum • Location where fiber tracts from (hindbrain) Medulla (decussation) spinal cord cross over oblongata • Autonomic reflex center • Heart rate / blood pressure • Respiratory rhythm • Vomiting / hiccupping / etc. Marieb & Hoehn – Figure 12.15

Marieb & Hoehn – Figure 12.19 Central Nervous System Central Nervous System

Brain Anatomy: Aggregation of loosely Reticular Activating System (RAS - functional brain system): clustered neurons:

Cerebrum (forebrain)

Lateral group Medial group Raphe nucleus • Raphe nuclei (midline) Diencephalon (midbrain) • Medial (large cell) group (small cell) visual • Lateral group Twisting of brain stem can stimuli lead to irreversible coma auditory LSD stimuli Brainstem Cerebellum (hindbrain) general stimuli

• Maintains cerebral cortical alertness (e.g., on / off switch) • Filters out repetitive stimuli (~ 99% of stimuli filtered…)

Central Nervous System Central Nervous System Meningitis: Brain Anatomy: Protection of the Brain: Inflammation of the meninges E. Cerebellum: 1) Bone (Skull – cranium portion) “Small brain” 2) Meninges (specialized connective tissue membranes) • Gray matter superficial; white matter deep (11% TBM)

• Precise timing of muscle coordination A) Dura mater (“tough mother”) C) (“gentle mother”) (balance, posture, repeated movements) Folia • Fibrous outer coating (2 layers) • Thin inner membrane Arbor vitae • All activity subconscious • Protects CNS • Contains blood vessels B) Arachnoid mater (“spider mother”) Cerebellar Processing: Two layers enclose • Delicate middle layer dural venous sinuses

Cerebral cortex • Nourishes CNS sends signal to move

Bone Dura mater (periosteal layer) Sensory information Dura mater Maintain from body (meningeal layer) body coordination Subarachnoid Arachnoid mater space (filled with CSF)

Pia mater Commands to motor neurons of spinal cord Marieb & Hoehn – Figure 12.17 Marieb & Hoehn – Figure 12.24

7 Central Nervous System Central Nervous System

Protection of the Brain: Constant internal environment necessary Homeostatic Imbalances of the Brain: Leading cause of accidental for proper neuronal functioning in brain death in North America 1) Bone (Skull – cranium portion) 1) Traumatic brain injury 2) Meninges (specialized connective tissue membranes) 3) Blood-brain barrier: Astrocyte-maintained barrier lining blood capillaries

Three layers of protection: A. Capillary endothelium B. Thick basal lamina C. Bulbous ‘feet’ of astrocytes • Signal tight junction formation Concussion Subdural hemorrhage Cerebral edema Alteration in brain function Bleeding into subarachnoid Swelling of the brain Tightly regulate substances following blow to head space via ruptured vessels bathing brain: In: glucose, amino acids, 2) Cerebrovascular accident selected electrolytes Third leading cause of death in North America Out: metabolic waste (urea), 3) Degenerative brain disorders proteins, toxins, drugs Ischemic stroke • Alzheimer’s disease Blockage of blood supply • Parkinson’s disease to brain due to blood clot • Displays differentially permeable (e.g., vomit center  brain stem) • Huntington’s disease • May be transient

Marieb & Hoehn – Figure 11.3

Central Nervous System Central Nervous System Protected by vertebral column / meninges Organization of Nervous System: Spinal Cord: • Provides conduction pathway to / from brain Nervous system • Contains major reflex centers Cervical region (8) Integration • Independently initiates patterns of motor (8) activity (e.g., walking) Central nervous system Peripheral nervous system Cervical (CNS) (PNS) enlargement Gross Anatomy: Motor Sensory Lumbar Thoracic output input • ~ 18 inches long (via vertebral foramen) enlargement region (12) • Two enlargements (cervical / lumbar) (12) Brain Spinal cord Motor division Sensory division Cornus (efferent) (afferent) • Innervation of limbs medullaris • Cord proper ends at L 1 Cauda Lumbar • Cauda equina (“horse’s tail”) equina region Autonomic nervous system Somatic nervous system • Spinal nerves (31 pairs) (5) (involuntary; smooth & cardiac muscle) (voluntary; skeletal muscle) (5) Sacral region (5) (5) Sympathetic division Parasympathetic division (1)(1) Marieb & Hoehn – Figure 12.29

Central Nervous System Central Nervous System Ascending tracts: Carry information to brain Spinal Cord: Spinal Cord: Descending tracts: Cross-sectional Anatomy: Carry information from brain Cross-sectional Anatomy: Posterior median sulcus Transverse tracts: Posterior Carry information across cord funiculus White matter

Central canal Lateral Gray funiculus matter

Characteristics: 1) Decussation present Anterior funiculus 2) Multi-neuron pathways Anterior median fissure 3) Somatotopy exhibited 4) Symmetrical arrangement Marieb & Hoehn – Figure 12.33

8 Central Nervous System Central Nervous System

Spinal Cord: Spinal Cord: Cross-sectional Anatomy: Cross-sectional Anatomy: Posterior median sulcus Posterior Posterior Dorsal Root funiculus horn White (interneurons) Dorsal root matter ganglion

Sensory neuron Central canal Lateral Lateral Gray Interneuron funiculus matter horn (visceral motor neurons) Motor neuron Gray Spinal commissure nerve

Anterior Anterior Ventral Root funiculus horn Anterior median fissure (somatic motor neurons)

Central Nervous System Central Nervous System

Spinal Cord: Homeostatic Imbalances of the Spinal Cord: Organization of Gray Matter: 1) Spinal cord trauma

Paralysis / Paresthesias Paraplegia Quadriplegia Damage to spinal cord leading Transection of spinal cord Transection of spinal cord

leading to functional / sensory loss between T1 and L1 between C4 and C7 2) Poliomyelitis 3) Amyotrophic lateral sclerosis (ALS)

Lou Gehrig’s disease

Destruction of ventral horn Progressive destruction of ventral motor neurons by poliovirus horn motor neurons (autoimmune?)

9